(I'm assuming that the response you are/were looking for wasn't the punchline for a joke.) I imagine what would make this work for a "Challenge Car" is what would not work for a street car, and that is, a cap might not be able to take repeated starts.

After thinking a bit more about this issue, you need to keep in mind that a battery isn't just used for starting a car...but for "working" the gauges and firing the ignition. I would think, that besides the question of wire gauge needed, what also would need to be worked out is providing the steady voltage to accesories if the race is "too long".

Such an ultracap could be useful if correctly integrated into the system.
But do not consider it as a 'bolt in' replacement for a battery.
Just like a battery, care and feeding (charging and discharge) must be done correctly in order to achieve long life.
As mentioned, you cannot exceed the maximum discharge amperage without damage.
And that max rate is determined by the specific design of the UC used.
A capacitor does not discharge instantaneously, instead at the rate is mainly determined by the charge voltage, the load resistance, and the internal resistance. The internal resistance is determined by the design of the unit. High amp devices require specialized (more expensive) construction.

Most UC are rated at 2.5V max, so you would be looking at an array of devices hooked up in series

I have been hit by a 1 farad capacitor, don't tell me they don't discharge instantaneously, (ok let's use the word instantaneously as a colloquial term and not a technical one, yes it will take a second, but a battery won't fully discharge for a much longer time.) Like I said you need resistance to stop it. and I doubt the starter would provide enough.

You can get some at very high end car audio shops. They are good for stabilizing ultra high wattage systems from power spikes from hits from subs.

Never help a redneck with a stereo system that requires more power than the vehicle needs to move.

Do the math. A Farad is a charge representing one amp in one second at one volt, or

(1 Amp / 1 second ) / 1 Volt

At 12V, 1.5 Farad ain't gonna start your car. It would be 18 amps (12*1.5) for a second. Your starter sucks down about 100 amps or better. So, 1.5 Farad would run your starter for a whopping fifth of a second. Give or take.

the cap will sure as heck be MUCH more expensive than a cheap battery. Most large audio caps I've seen are almost as large as a 51 series battery (honda civic size). Better off with a 51 batt than a cap IMO

FlightService wrote:
...Capacitors will completely discharge instantaneously. I doubt the starter would act as a resistor enough to slow the discharge...

A common mispreception. They're no different from a battery if you drop a wrench across the terminals. Both they and a battery provide as much current as their internal and external load resistance permits -> Ohm's law.

As was said, it's all about energy density, and since a capacitor is much less than a battery per pound, it's a pointless exercise. Just get a Odyssey PC680 and be done with it.

Zomby woof wrote:
I drive a car where removing 25 lbs makes a noticeable difference, so I've been looking into lightweight batteries, and (being cheap) will build my own in a few weeks.
It should have no problem running the car, and will weigh about 2 lbs.

Zomby, take pix and start a thread when it's done. That's going to be interesting.

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